Computing devices can be used to recognize faces, voices, handwriting, and other objects and patterns. In a typical implementation, a computing device can continuously monitor an input stream or receive a batch of input data. This input stream may be, for example, a video stream from a video camera or an audio stream from a microphone. The computing device can determine whether a portion of the input stream is likely to contain information corresponding to the target item, object, or pattern to be detected. For example, the computing device can make a preliminary determination as to whether a particular portion of the input stream includes to any face, any speech, or any handwriting at all. Once the computing device has made this preliminary determination, the computing device can then perform other processing or cause other processing to be performed. The computing device may perform recognition of which particular face, voice, or other target is present in the input stream in addition to detecting whether any face, voice, etc. is present in the input stream.
A user's experience with the above detection system can be defined in terms of performance latencies and detection errors. These can include false acceptances and false rejections. False acceptances occur when the detection system erroneously hypothesizes from the input data that the user is trying to initiate communication with the computing device. False rejections occur when the detection system fails to respond to user communication directed at the computing device. Detection systems may use the concept of a confidence score when detecting the target item, object, or pattern. Higher confidence in the accuracy of the detection can be reflected by a higher confidence score, while lower confidence in the accuracy of the detection can be reflected by a lower confidence score. The detection system may use an operational threshold, such as a confidence score threshold, to help determine when the target item has been detected. If the detection system determines that the operational threshold has been met, additional processing can occur.